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authorDave Chinner <dchinner@redhat.com>2010-09-22 10:47:20 +1000
committerAlex Elder <aelder@sgi.com>2010-10-18 15:07:44 -0500
commite176579e70118ed7cfdb60f963628fe0ca771f3d (patch)
treee2d252fcd692aa4e3907300521e2af81c974f875 /fs/xfs/xfs_ag.h
parentbd32d25a7cf7242512e77e70bab63df4402ab91c (diff)
downloadlinux-e176579e70118ed7cfdb60f963628fe0ca771f3d.tar.bz2
xfs: lockless per-ag lookups
When we start taking a reference to the per-ag for every cached buffer in the system, kernel lockstat profiling on an 8-way create workload shows the mp->m_perag_lock has higher acquisition rates than the inode lock and has significantly more contention. That is, it becomes the highest contended lock in the system. The perag lookup is trivial to convert to lock-less RCU lookups because perag structures never go away. Hence the only thing we need to protect against is tree structure changes during a grow. This can be done simply by replacing the locking in xfs_perag_get() with RCU read locking. This removes the mp->m_perag_lock completely from this path. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Alex Elder <aelder@sgi.com>
Diffstat (limited to 'fs/xfs/xfs_ag.h')
-rw-r--r--fs/xfs/xfs_ag.h3
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/xfs/xfs_ag.h b/fs/xfs/xfs_ag.h
index 4917d4eed4ed..51c42c202bf1 100644
--- a/fs/xfs/xfs_ag.h
+++ b/fs/xfs/xfs_ag.h
@@ -230,6 +230,9 @@ typedef struct xfs_perag {
rwlock_t pag_ici_lock; /* incore inode lock */
struct radix_tree_root pag_ici_root; /* incore inode cache root */
int pag_ici_reclaimable; /* reclaimable inodes */
+
+ /* for rcu-safe freeing */
+ struct rcu_head rcu_head;
#endif
int pagb_count; /* pagb slots in use */
} xfs_perag_t;